Bimetallic electric thermostat



Patented Sept. 3, 1940 UNITED STATES PATENT OFFICE tion of Delaware lease Corporation, Jersey City, N. J., a, corpora- Application December 4, 1937, Serial No. 8,185

'7 Claims.

This invention has for its principal object the production of an exceedingly inexpensive and simple thermostatic device which shall be adapted to detect and give a visual or audible indication,

alarm, of the presence of excessive heat due, for instance, to a fire. By preference, the device may be detachably mounted on the ceiling of a room or other enclosure, the heated air naturally tending to flow upwardly, as is well known.

A further object of the invention is the production of a device of the above character which shall be so constructed as to occupy a very small space only.

A further object of the invention is the production of a thermostatic device having the above characteristics which shall be adapted to operate on the principle of the difierence in the rate of expansion of two metallic strips or bars of different masses when they are subjected to the influence of heat. Accordingly, the device is peculiarly adapted in its application for the detection of a quickly acting fire where the temperature rises suddenly on what is known as the rate-of-rise of temperature principle in contradistinction to a gradual and more or less uniform rise in temperature and depending for operation on the attainment of a predetermined fixed temperature. The thermostat, however, is

so constructed as to also be actuated upon the attainment of any predetermined fixed temperature and irrespective of its rate of rise.

By preference I utilize two coiled strips of planished metal which may be concentrically disposed with relation to each other in the interest of economy of space, one end of said strips being fixed and the other end thereof movable whereby the expansion of said strips by the action of heat and the consequent partial uncoiling of the strip will complete an electrical circuit which includes a signal and source of power and thereby energize the signal.

The planished metal strips employed preferably comprise two metals united by riveting or brazing to form bimetallic strips, one of said metals possessing a relatively high co-efiicient of expansion and the other a relatively low coefficient of expansion. When exposed to heat or temperature rise the metal having high expango sive properties which may be any suitable metal or an alloy of metal, of necessity expands or lengthens while the other metal of which the metallic strip is composed and which may be brass, inasmuch as it has low expansive properties, will have little or no movement. The result by the energization of a. signal or is a bending or uncoiling of the strip around a fixed point, such as the fixed endof the strip, in the specific embodiment of the invention illustrated. After expansion, and when the temperature again recedes, the high expansive metal automatically shrinks back to the contour it originally assumed. The thermostatic device may thus be said to be self-restoring so that the length of its life accordingly is indefinite.

A practical embodiment of the invention is illustrated in the accompanying drawing in which:

Fig. 1 is a plan view of the device showing the cover partly broken away to expose the contained parts a portion of which are shown in section. 15

Fig. 2 is a horizontal section taken through the device, and

Fig. 3 is an enlarged section taken through one of the bimetallic strips.

Referring in detail to the several figures of the 20 drawing:

Either one of the bimetallic strips which, as shown in section in Fig. 3, are composed of two parts to wit: an outer strip of metal having high expansive properties and indicated at I0 25 and which may be composed of any suitable metal or an alloy of meta-l, and an inner strip ll having low expansive properties which may be of any suitable metal such, for instance, as brass. These two strips are united together 30 preferably by riveting, brazing or welding to form complete units and the joined strips forming the units or elements are partially coiled and then heated so as to retain their coiled contour.

The two bimetallic strips or units are identical in construction but the inner one, which is indicated at I2, is of relatively smaller width and mass than the outer bimetallic strip which is indicated at IS. The inner strip l2 accordingly is more susceptible to changes in temperature than the outer bimetallic strip. The outer or heavier bimetallic strip is fastened at one end, as by a screw 14, to a block l5 of insulating material which forms a part of or is attached to an insulating base it comprising the support for 45 the thermostatic device of the invention. The base 16 is provided with a protective cover plate ii having a plurality of perforations it to permit heated air to reach the thermostatic strips described. The cover ii is suitably and detachbly do fitted to the base it by the screws i8 shown.

An end view of the inner bimetallic coiled strip I? or that of smaller mass is also secured to the block it, as by the screws ill. The secured end of said inner strip i2 may be provided with a contact plate and the inner side of the outer strip l3 adjacent its free end may be provided with a contact strip 2|. A variable or adjustable contact screw 22 is carried by the free end of the outer strip l3 and is adapted to be brought into contact with the contact plate 20 while the free end of the inner bimetallic strip I2 carries a variable or adjustable, contact screw 23 which is adapted to be brought into contact with the con tact plate 2| One terminal of an electric circuit 24 is connected, as shown, to the fixed end of the bimetallic strip [2 while the other terminal is connected to the fixed end of the bimetallic strip l3. Said electrical circuit includes a battery 25 and a signal, 26, either audible or visual, and of any suitable construction which is adapted to be energized when the circuit is closed. Obviously, however, the device may be operated either on an open or closed circuit by change of the contact screws in the bimetallic strips l2 and I3.

The inner bimetallic strip l2 having the least mass and therefore being the most sensitive to changes in temperature is adapted to operate upon a sudden rate of rise of temperature occasioned, for instance, by the heat from a quickly acting fire. In that case the strip 12 tends to straighten out and consequently partially unwinds or uncoils in a counterclockwise direction to thereby b g the end of the contact screw 23 into engagement with the contact plate ,2! and thereby complete the circuit through the outer bimetallic strip I3 of heavier mass and in an obvious manner. When the operation of the device depends on the attainment of a fixed or predetermined temperature, however, occasioned for instance by a slow starting fire increasing gradually in intensity, both bimetallic strips Will expand or uncoil with approximate uniformity. In thiscase the circuit will be closed to energize the signal by the engagement of the end of the contact screw 22 with the plate Hi, the cricuit then being completed directly through the outer or heavier bimetallic strip I 3 with the inner or lighter bimetallic strip circuit. As is obvious, when the bimetallic strips cool after being subjected to any heating effect, they contact and assume their original contour and position and at the same time break the circuit to de-energize the signal. The thermostat thus is a self-restoring one and may be used any number of times without adjustment and without replacement of parts. Furthermore coiling of the bimetallic units or elements and mounting them in' concentric relation with respect to each other permits the deviceto bemanufactured and installed in a conveniently compact and spacesaving form. In practice I have found it feasible to construct the inner or smaller strip l2 of about I0 per cent of the mass of the outer or heavier strip l3 although the difference between the masses of the strips may be varied considerably to meet varying or difierent conditions and depending also on the metals or alloys employed in the construction of the strips.

The invention claimed is:

1. An electric thermostat comprising two metallic coiled elements each consisting of two strips of metal united together one of which strips has a high coefiicient of expansion while the other has a low coefiicient of. expansion, one end of each of said elements being free and the other endfixed and in circuit with a source of current supply and a signal with the free ends of each of said elements being movable and adapted to engage the l2 forming no part of the other element to close the circuit and energize the signal when said elements are subjected to 'the influence of heat, one of said elements being less than a full convolution thereby providing a gap between its ends and the other said element being greater than a full convolution and projecting through said gap of the first said element 50' as to make contact in operation at the inside of the first said element.

2. An electric thermostat comprising two coiled jected to the influence of heat, one of said elements being less than a full convolution so as to provide a gap between its ends and the other said element being greater than a full convolution and having its movable end projecting through said gap of the first said element so as to make contact in operation at the inside of the first said element.

3. An electric thermostat'comprising two metallic coiled elements of different masses mounted in concentric relation to each other, said elements each consisting of two strips of metal united together one of which has a high coeflicient of expansion while the other has a low coefiicient of expansion, one end of each of said elements being fixed and in circuit with a source of current supply and a signal and the other ends of said elements being free and movable each toward the other element to close the circuit and energize the signal when said elements are subjected to the influence of heat, one of said elements being less than a full convolution thereby providing a gap between its ends and the other said element being greater than a full convolution and projecting through said gap of the first said element so as to make contact in operation at the inside of the first said element,

4. An electric thermostat comprising two stripsof different masses the larger one of which is adapted to expand slowly in response to a gradual temperature rise and the smaller one of whichis adapted to expand prior to the expansion of the larger strip when the thermostat is subjected to a sudden rate-of-rise of temperature, said strips being in circuit with a signal device and adapted for contact each with the other to close the circuit,

one of said strips being arranged inside the other and provided with a gap and the other strip being provided with a free endextending through said gap adapted to contact with said first-named strip to close the circuit and energize said alarm when said second-named strip has reached a predetermined temperature.

5. An electric thermostat provided with a support and two coiled metallic elements of different masses mounted on said prising two strips of metal united together, each said strip having appreciably difierent coefiicients of expansion, one end of each of said elements being fixed and in circuit with a source of current supply and a signal and the other ends of the ele-- ments being free and each adapted to close toward the other and thereby in either event close said circuit and energize said signal upon a rise of temperature, one of said elements being less than a full convolution thereby providing a gap between its ends and the other said element besupport and each coming greater than a full convolution and projecting through said gap of the first said element so asto. make contact in operation at the inside of the first said element.

6. An electric thermostat provided with a base having an upstanding block and two metallic coiled elements of different masses mounted on said block in concentric relation to each other, said elements each comprising two strips of metal united together one of which. has a high co-efiicient of expansion while the other has a low co-eflicient of expansion, one end of each of said elements being secured to said block on opposite sides thereof and in circuit with a source of current supply and a signal and the other ends of said elements being free and movable each toward the other element to close the circuit and energize the signal when said elements are subjected to the infiuence of heat, one of said elements being less than a full convolution thereby providing a gap between its ends and the other said element being greater than a full convolution and projecting through said gap of the first said element so as to make contact in operation at the inside of the first said element.

'7. An electric thermostat provided with a base, an insulating block mounted thereon, a removable perforated cover detachably mounted on said base and two metallic coiled elements of difierent masses concentrically positioned within said cover, said elements each comprising two stripslof metal united together one of which strips has a high co-efiicient of expansion while the other has a low co-efiicient of expansion, one end of each of said elements being free and the other end secured to said insulating block and in circuit with a source of current supply and a signal with the free ends of said elements being movable and adapted to engage the other element to close the circuit and energize the signal when said elements are subjected to the influence of heat, one of said elements being less than a full convolution thereby providing a gap between its ends and the other said element being greater than a full convolution and projecting through said gap of the first said element so as to make contact in operation at the inside of the first said element.

ERNEST A. LOWE.

CERTIFICATE OF CORRECTION. Patent No. 2,215,526. September 19m.

ERNEST A. LowE.

It is hereby certified that the name of the assignee inthe above mimbered patent was erroneously written and printed as Airelease Corporation" I whereas said name should have been written and printed as "The Airelease Corporation, ofJeI'sey City, New Jersey, a corporation ofDelaware, as shown by the record of assignments in this office; and that the sold Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office. I

Signed and sealed this 8th d of October, A. D. 191m.-

Henry Van Arsdalee;

(Seal) Acting Commissioner ofPatents.

should be read with this correction therein that the same CERTIFICATE OF CORRECTION. Patent No. 2,213,526. September 5; 191m.-

ERNEST A. LOWE.

It .is hereby certified that the heme of the assignee inthe above mim bered patent was erroneously writterl and printed as whereas said name should have been written and printed as Corporation,

"The Airelease a. corporation of Delaware, as shown by the record of assignments in. this office; and that the ssid Letters Patent ofJeI'sey City, New Jersey,

the record of the case inthe Patent Office. 4

Signed and sealed this 8th dgy of October, A. 1;. 191m.-

Henry Van Arsdale;

(Seal) Aoting Commissioner of Patents.

Airelease Corporation" I may conform to 

